1. Technical Field
The present invention relates to a liquid developer and an image forming apparatus, and in particular relates to a liquid developer and an image forming apparatus that can use the liquid developer.
2. Related Art
As a developer used for developing an electrostatic latent image formed on a latent image carrier, a liquid developer (liquid toner) is known. Such a liquid developer is obtained by dispersing toner particles in a carrier liquid (an insulation liquid) having electric insulation properties. The toner particles are formed of a material containing a coloring agent such as a pigment or the like and a binder resin.
Conventionally, a synthetic resin such as a polyester resin, a styrene-acrylate ester copolymer and an epoxy resin or the like is used as a material for constituting the toner particles used in the liquid developer. The toner particles containing such a resin are easy to handle. Further, in the developing method using the liquid developer containing the toner particles, it is possible to produce an image having good color development with high fixing characteristic.
However, in the conventional liquid developer, the resin constituting the toner particles described above has low affinity with the insulation liquid. Therefore, it is difficult to make the toner particles disperse in the insulation liquid sufficiently.
In order to improve the dispersibility of the toner particles in the insulation liquid, it is attempted that a rosin resin having high affinity with the insulation liquid is used as a resin constituting the toner particles. One example of such a liquid developer is disclosed in JP Patent No. 3332961.
However, in the liquid developer disclosed in the above document, although the toner particles containing the rosin resin have good dispersibility in the insulation liquid at the early stage of the preservation of the liquid developer, aggregation of the toner particles is likely to occur during the preservation with the elapse of time. Therefore, there is a problem in that it is difficult to keep the good dispersibility of the toner particles in the insulation liquid for a long period of time. Further, there is another problem in that such toner particles used in the conventional liquid developer do not have sufficient charge property (in particular, positive charge property).